The BOREAS Information System

BOREAS Investigators will be back in the field for four campaigns in 1996. There will be a limited winter campaign (FFC-W '96, February), a small spring/thaw campaign (IFC-1 '96, April), a large summer campaign (IFC-2 '96, July), and a large autumn campaign (IFC-3 '96, October).

Major Shortcomings in the 1994 Data

• Beginning and end of the growing season: We do not have a clear picture of how the boreal forest system emerges from winter and closes down for winter. IFC-1 started in May 1994, but many coniferous species had already started photosynthesis. IFC-3 ended in late September 1994, but photosynthesis was recorded through November 1994, and respiration fluxes were measured in the NSA throughout the winter of 1994 - 1995. The bulk of the 1994 measurements did not extend through the thaw and freeze-up periods, leaving a significant gap in our understanding of the processes controlling carbon and energy fluxes as these times.

• Role of moss: Analysis of some field measurements and some preliminary modeling studies indicate that the moss layer may play an important role in carbon assimilation, particularly in the wet coniferous sites. The data gathered in 1994 was not sufficient to construct a credible model of moss photosynthesis and water relations. More detailed measurements which extend over the growing season are needed.

• Smoke in IFC-2: Heavy smoke from forest fires alternating with patchy cloud cover severely reduced optical remote sensing opportunities in IFC-2, the mid-growing season field campaign. All of the airborne remote sensing data collection work was compromised to some extent. Of the data gaps, perhaps the most serious is the suite of C-130 measurements, particularly the incomplete MAS and ASAS data acquisitions over the NSA. The result is that we do not have a complete remote sensing record of the growing season to match up with our surface flux observations and other data sets. This seriously compromises the development of algorithms for growing season (maximum) Fpar and LAI.

• Snow cover and the radiation balance: Preliminary modeling work indicates that the effects of the forest canopy on albedo may be highly significant in determining the winter climatology of the northern mid- and high-latitudes, see Bonan et al. (1992, 1995). This suggests that replacement of the boreal forest by a low-lying vegetation cover (a northward migration of biomes due to global warming and drying) would result in a large increase in the wintertime albedo over the northern high latitudes and dramatic changes in the climate there. The increase in albedo would decrease winter and summer temperatures at these latitudes which may partially counteract the classical "greenhouse effect" which is predicted to generate a significant warming for the same area.
  The current correlation of climate indices and biome boundaries in the boreal zone is a result of a two-way interaction between the biota and the physical climate system there rather than solely a consequence of (one-way) atmospheric forcing. These simulations were performed using a land surface parameterization coupled with an Atmospheric Generation Circulation Model (AGCM) which incorporated a fairly basic description of snow-vegetation-albedo effects. The uncertainty attached to this result is large, mainly because we do not have enough information about the physics of radiative transfer within snow-covered boreal vegetation and also because we do not know how to spatially assign albedo fields for the region from satellite data.

• Winter snow reflection in the boreal forest: As yet, we have little useful surface and airborne data to help us understand how the snow-covered forest intercepts and reflects/emits incoming solar and longwave radiation. During the winter of 1993-1994, most of the forest appeared to be very dark, particularly at low view angles. This is true even for deciduous areas, where low solar angles in winter compensate for low stem densities with the result that the bulk of the solar radiation appears to be intercepted by stems and bare branches. By contrast, the agricultural areas to the south and the tundra to the north of the forest appeared to be almost completely snow-covered and were highly reflective.
  To what extent does the radiation balance of the surface correspond with this visual impression? Can we quantify them using satellite data? The radiation sensors on the Automatic Meteorological Stations (AMS) in BOREAS-94 were not equipped with snow blowers or alcohol sprayers so much of their data from early 1994 (the systems came on-line in March 1994) are suspect. The complete set of these anti-frost devices were only installed before the winter of 1994-1995. In addition, we do not have a complete optical remote sensing data set, consisting of surface (PARABOLA) and airborne (ASAS, CASI) data, over the snow-covered SSA radiative transfer test sites from the 1994 focused field campaigns. Compilation of this data set with supporting ground truth (snow depth, snow water equivalent) measurements would be a primary goal for a winter focused field campaign in 1996 to address the issues described above.

Open or Unresolved Issues From BOREAS 94

• 1994 was a record warm, dry year: 1994 was a record frost-free year for the SSA and the driest year on record in the NSA. Since 1994 was characterized by high temperatures and high vapor pressure deficits, it may have provided us with an image of the transient behavior of the boreal forest with respect to global change rather than a representative baseline for the status quo. The representativeness of the 1994 field year would have been a discussion issue in any case, but the fact that 1994 was so exceptional leads us to suspect that we may be seeing something more relevant to the future of the system rather than obtaining a clear picture of its current functionality. The anomalous meteorological conditions of 1994 can be expected to influence many aspects of the BOREAS-94 data set in addition to vegetation responses; for example, the TGB group is expected to show some evidence that the long, warm growing season led to an unusual time-profile of soil/wetland CO₂ and CH₄ fluxes in the SSA.

• Positive surface-atmospheric boundary layer drying feedback: The development of deep dry boundary layers suggests that a positive drying feedback may be at work in this region at the beginning of the growing season when the soils are still partially frozen (see Betts et al.; in press) and also during warmer periods when the vapor pressure deficit feedback effect becomes important. We believe that we have the data from BOREAS-94 to make some headway on determining if this model holds up for the warm, dry conditions of 1994. If this turns out to be true or partially true for 1994, which is likely, to what extent would it hold for more 'normal' conditions? If this feedback system is the norm, it implies that the result of the vegetation's conservative water-stress avoidance strategy in the region is to exacerbate the degree of external stress. Teleologists would propose that this implies that the ecosystem is out of sync with its climate while strict Darwinists (Dawkins faction) might argue that this apparent reduction in ecosystem efficiency is to be expected from game theory. More data for a different kind of year would help to resolve some of these issues.

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